Objectives: Major emphasis is placed upon the study of tumor antigens of the transplantation rejection type (TSTA), and of tumor antigens (TA) assayed by in vitro techniques and of the immune responses they evoke. As a corollary to this study the biologic properties in vitro and in vivo of histocompatibility (H-2) antigens are under study. Solubilization and methods of purification of both TSTA and H-2 are under investigation with the ultimate purpose of defining these membrane antigens after purification in physico-chemical, biologic and molecular terms. The role of a B-tropic retrovirus as a vector in the transmission of genetic information of a specific tumor antigen (TSTA of Meth A) is under study as well as the use of TSTA markers (Meth A) in the hope of defining more clearly the molecular events in transfection studies using DNA of chemically-induced sarcomas.